Submarine telegraph cable



Jan. 8, 1935. R L, PEEK, JR 1,987,416

SUBMARINE TELEGRAPH CABLE Filed Feb. 20, 1929 //v VENTOQH R L. FEE/(JR.

ya/g zww A TTORNE Y Patented Jan. 8, 1935 '7 UNITED STATES PATENT OFFICE SUBMARINE TELEGRAPH CABLE Robert- 1.. Peak, Jr., Union, a. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N.H Y.,' a corporation of New York Application" February 20, 1929, Serial No. 341,368

' 1o o1aims, (01. 173264) This invention relates to submarine telegraph cables and more particularly to deep sea submarine cables of light and simplified construction for use under conditionsiwhere a light service demand necessitates low cost of construction and laying. V a

It has been-found thatthere is a demand for telegraph service between points, separated by deep oceanic waters, where the trafllc would be too low to justify the expense of laying a submarine cable of the type in which an outer armorin'g is placed about the insulation to provide the necessary tensile strength of the cable during laying operations or during lifting operations for repairs.

-I-t has before been proposed to';eliminate"the outer armoring from'deep sea cables and to place light, steel armor wires directly about the conductors, thereby providing a metallic core of sufficient tensile strength to sustainthe weight of the cable while it is not resting on the sea bottom. Ithas'also been proposed to substitute for the 'u'sual' outer steel armoring a wrapping of hemp' or like material which would provide the necessarytnsile strength during the laying" op erations. It has furthermore been-proposed to substitute for some or all of the outer steel armor w-iresstrands of light metal, such as aluminum,

or' of f more copper;

i In accordance with the present invention a deep sea cable is constructed with a central conductor l of "one'or more non-magnetic metals or alloys of suflicient'conductivity to provide for a-limited traflic and having-such lightweight and high tensilestrength that the conductor is capable of sustaining the total weight of the cable during the process of layihg'in the sea' so thatanouter armoring around the insulation will not be required for'this purpose, even at depths as great as-2 to 2 nautical miles. f

The central conductor in accordance with this invention may be composed entirely of hard drawn aluminum-or of an aluminum'alloy of high ten-"- "sile strength, which will'have suflicient'conducmay to serve in a low speed telegraph system. The conductor may furthermore comprise a combination of strands, some of which are made of valur'n'ii'n rrror of the alloys thereof, referred to, and others of which may be either of hard drawn copper or a copperalloy of high tensile strength. By'su'c'h a combination of metals the average conductivityof the stranded conductor maybe high ,.,.enough 'tofrij eet the particular service require-v nients'andits' strength at the sa'metime' may be maintained at a value which will permit of laying in comparatively deep water without danger of breakage.

In thefollowing description reference will be made to the accompanying drawing which shows a portion of a submarine cable to which the present invention may be applied.

In, the design of submarine cables the question of cost is extremely important. Since the cost is directly related to the dimensions of the several elements within the cross section of the cable, itis imperative to consider with the utmost care even the slightest dimensional changes in the cross section as well as the choice of materials. This is especially true in the case of telegraph cables where the service is not exacting and the revenue low, that is, where the traflic amounts to say only 200 words a minute, at simplex operation over distances of 1000 miles or more. This class of service may of course include cables of somewhat shorter length with a corresponding increase in traffic capacity;

Cables of this type must therefore be reduced to minimum dimensions and must be of the simplest possible construction. Due to the low signaling frequency, loading of the conductor with magnetic material is not necessary and the I sklneiiect is negligible. For the deep sea porhighly conducting metal, such as 1 i i also be dispensed with and a braiding may take tions of such cables the outer armoring should its place for the protection of the insulation. It is consequently necessary to construct the cable with a metallic conductor, which not only meets the traffic requirements, but which also is capable ofsustaining the weight of the cable in water during laying operations over depths which frequently maybe as great as 2% miles or even more, which means that when the usual safety factor of 2 to 3 is applied, the cable must be able tocarry its own weight in water at a hypothetical depth as great as 5 to 7 miles. I'his hypothetical depth'will be referred to hereinafter as the breaking length of the cable, or of any particular strand thereof, and is the length which the cable or strand is just able to sustain at the verge of breaking when it is suspended vertically in water.

To provide ,a given resistance of the conductor per unit length of cable, as required by the estimated traflic, the designer may choose from a limited number of metals for the conductor. The cost of'the metal proper is of course important and the overall diameter of the conductor, which for a given resistance depends upon the specific conductivity of the metal, greatly influences'the be proportional to the diameter of the central conductor, which determines the; innerrdiameten of the insulation. The electrical resistance of the cable is inversely proportionalto thecross sectional area of the conductorv and directly to the resistivity of the metal or metals composing the conductor. From these considerations. itsv is apparent that the substitution of a, metal, of,

higher resistivity for one of lower resistivity in thecentral conductor will necessitate anincrease, the diameter, of the conductor and apropertional increase in the outer diameter of thein sulation, and hence results in aconsiderable increasein. the total amount ofinsulation and in thecost-of the cable, whena given trafiic capac-fl that such a conductor shouldhave, the lowest possible average electrical resistivity, consistent. with. such strength.

The choice of metals thus involves the consid eration of their tensile strength relationjto,

their, weight. per unit volume in. water, which relation. is expressed by the breaking lengthof.

the metals. The weight of. theinsulating ma- 'terialsand of the braidingmaterials may:- bedise regarded in these considerations since thein specific, gravity. usually is close to 1 and they therefore do not. add tothe weight of the cone ductori in water. i i .Thefollowing table contains, beside other data,

the conductivityinper. centv of that. of. purev annealed: copper and,v the breaking length, of, a.-

number of. metals andalloys which are suitable-- for-submarine conductors.

Table I I 001111116? .Specific. Tensile Breaking Material tivity gravity strength length,

' i 1 in water (lbs/sq. in.) (nautsrXf Annealed copper. 100 7.9 15,000 .72 Hard drawn'copperun 97 7. 9 60,000 2. 89 Cadmium bronze 85 7.9 78,000 3.76 Hard drawn aluminum. 1. 7 28, 000 6; 32 Aluminum alloy No. 2. 55 1.7, 48, 000. 10.89 Aluminum alloy No. 1 35 1.8 70, 000 14.9 Elektron 35 .8 32, 000 15.8' High carbon steel N 1 6.9-1 120,000; 6. 62: High carbon steelNOr 6. 9 I 180, 000 9-. 9,

Aluminum alloy N o. 2 contains-aluminumand2 less--than 2,-% ofmagnesiumand silicon. Alu,--v

min-um alloy No. 1, consists of, approximately- 94.3% aluminum, 4% copper, 0.8% manganese, 0.6%, magnesium, and 0.3 silicon. These com.- pdsitionszarerepresentative of ,two distinct types of men known, a1u1ninum..alloys. 7

Hard drawn aluminumandalloy No. 2. COm'ri reductionin weight; of i more. than.50.%..,., Thisooir.

binef a fairly high conductivity with, highlbreake ing lengthand may therefore, in accordance ,with', the invention, be, used exclusively for the, conduc,,

tor, at ,a,,depth, oLmore than} ,miles and where;

"inaterial'may be determined from the left hand section of Table II below in accordance-with-the the tramc is low enough to not require an excessively large diameter of the conductor with a consequent unreasonable cost of insulating material. In order to reduce the size of the conducting strand, when desired, high conductivity metals such as hard drawn copper or cadmium bronze may be used, in accordance with this invention, with either hard drawn aluminum. or alloy No. 2 to-provideconductors of suflicientcbreaking length for different laying depths.

I As an example, a cable may be assumed, such asshown in the drawing, where the conductor 10 issurrounded byva heavy layer of insulation 11 of any suitable material which in turn is protected'byany suitable braiding 12 of light and tough, water resistant material such as hemp.

The "conductor may consist of '7 strands of equal si'zaaand: 'of-i' hardidrawn copper and aluminum alloy No.. 2. The number of strands of each requirements for: conductivity and breaking,

-- .TableiIl" Conducting core of hard drawn Conducting core of hard drawn copper-and highcarbon steel No. 2

coppenand aluminum alloy; No. 2

No. of strands i Break- 1 ing No. OfEStIEHdSL Breaking Con: length ductivi- 'c ty. (nauts.)

Con: length ductivi ot-core ty'(%)-- (nauta) num alloy High carbon steel -No. 2

' Hard drawn Hard drawn copper For-thesake of comparisomTabl'ezIlialso con tainsdata. for the; conductivity and breaking: length ;cf; conductors, of 10 strandsmade of. hard; drawn; copper and, high carbon steel No. 2z of; highgtensile; strength, the: entries being so: are ranged, that the breakingilengths; of the: ooppere steel-, conductors closelyapproximate thosenf cor-'--- responding copper-aluminum conductors in the:v left hand portion of Table II. The conductivityof steel is largely dependentupon the carbon contentandhmayvary up to 10%. ofpthat. of copper;;,

this, variation affects the total conductivity; 8S:

indicated by the limiting figures, in the. table;v

--From a, comparison-of the, conductivity of the:

1 two ,types of conductors, at similar breaking;

- lengths, it 'becomes apparent that theg-advantage;--.

of. thecopperaluminum conductorroverthecop per-steel conductor; increases as the breaking,

length increases.- Thus at. alaying-depth of 2-.

7 miles, corresponding to abreaking length of about;v

centage is attained. Calculations. furthermore. show that the weight ratio inwater of the C011,"

per-aluminum. and, copper. steel conductors. offr.

breaking lengthtof, 5.5 is as, 3.47,, to 77.5.. or. a

course means. much:.easier. handling: during, the

' laying, operation, lighter, machinery, and thelneed;v ofonly comparatively small boats. Suchareduc:

tion in weight of course is of extreme advantage at great laying depths where a very great length of cable must be held suspended during the laying operations.

Similar considerations show that cadmium bronze may be used instead of copper in a cable such as described above. For a given breaking length a smaller proportion of aluminum alloy No. 2 may then be used or this alloy may be replaced by hard drawn aluminum. Various other combinations of copper, aluminum and their alloys are possible within the scope of this invention. The desired combination may be attained with the strands of equal size, or of different sizes, or in any other desirable manner, as for example by drawing the two desired metals in the proper proportions into a single strand. It is also contemplated that a given cable may have different sections with different combinations of metals making up the central conductor and may be of difierent constructions. Thus the proportion ofhigh conductivity metal to high tensile strength metal may be made smaller in sections at smaller depths than in those at greater depths, and shore sections may furthermore be armored in the usual manner with an outside armoring.

In the case of cables to be placed in tropical waters and in which the insulation is protected from teredo attack by a sheathing of metal the weight of this sheathing must of course be taken into consideration in determining the load on the core, since this sheathing usually does not add to the tensile strength of the cable. The outer braiding, on the other hand may be of such design and materials that it would aid materially in supporting the cable during lifting or laying operations, so that the strength requirements of the conducting core may be reduced.

What is claimed is:

1. A signaling cable for laying in the sea to depths of about two miles or more, comprising a central nonmagnetic composite conductor and insulating material surrounding said conductor, characterized in this that the metallic composition of said conductor comprises separate aluminous and cupreous metals in such proportions that the average conductivity of the total conductor is more than 50% of that of annealed copper and that the breaking length of said conductor is about four miles or more so that the conductor is capable of safely sustaining its own weight during laying in the sea to said depth.

2. A signaling cable having sufficient tensile strength for safe laying in the sea to depths of about two miles or more, comprising a central non-magnetic composite conductor and an insulating sheathing surrounding said conductor, said conductor being composed of separate aluminous and cupreous metals in proportions such that it has an average conductivity of more than 50% of that of annealed copper and has a breaking length of about four miles or more so as to be capable of sustaining its own weight during laying in the sea to said depth without the support of an outer armoring.

3. A deep sea signaling cable, comprising a conducting center and a. surrounding insulating sheath, said conducting center being composed of separate elements of aluminum and copper in such proportions of volume that the average conductivity of said center is at least 50% of that of annealed copper and that the breaking length is about four miles or more.

4. In a submarine cable, a metallic core and an insulating sheathing surrounding said core, said core comprising a strand of aluminum alloy containing manganese and silicon in an amount not to exceed 2%.

5. A submarine signaling cable for laying at great ocean depth, comprising a metallic core and insulating sheathing thereabout, said core comprising at least one strand of a metal with copper as its main constituent and another metallic strand with aluminum as its main constituent and having a conductivity of more than 35% of that of annealed copper, and the proportion of one kind of strand to the other kind of strand being such that said core has a breaking length of about four miles or more.

6. A deep sea cable for laying at a depth of about two miles or more, comprising a central conductor for telegraph signaling and a sheathing therearound having high insulation resistance in sea water, said conductor including at least one strand of a metal with copper as its main constituent and another strand of an aluminum alloy having a conductivity of more than 35% of that of annealed copper, and the proportion by volume of said metal to said alloy in said conductor being such that it has a breaking length in the sea of more than five miles.

'7. In a submarine cable, a metallic core and an insulating sheathing thereabout, said core comprising at least one strand of cupreous metal and another strand of aluminum alloy containing manganese and silicon in an amount not to exceed 2%.

8. A submarine cable core having a safe breaking length for laying in the sea to a depth of about two miles or more, comprising a conducting center having a conductivity of at least 50% of that of annealed copper and an insulating sheath enveloping said center, said conducting center being non-magnetic and composed of at least 20% by volume of an aluminous metal and less than by volume of a cuprous metal.

9. In a deep sea submarine signaling cable, a non-magnetic metal core and an insulating sheath about said core, said core being composed of a continuous element of cupreous metal and another continuous element of aluminous metal and having suflicient breaking length to sustain the weight of the cable without the aid of armoring dun'ng laying in the sea to depths of about two miles or more with a safety factor of about two or more.

10. An armorless deep sea signaling cable, comprising a conducting center and a surrounding sheath having high insulating resistance under sea bottom conditions, said conducting center being composed of separate elements of aluminum and copper in such proportions of volume that the average conductivity of said center is at least 50% of that of annealed copper and that the breaking length is about four miles or more.

ROBERT L. PEEK, JR. 

